Field of the Invention
The present invention(s) relate to image processing that reduces the influence of scattered light.
Description of the Related Art
In the field of surveillance cameras and the like, there is a problem in that visibility is reduced due to the influence of particles (for example, fog or mist) existing between a camera and an object, and the image quality of a captured image is degraded. A cause of this is that light is scattered by particle components when the light passes through the atmosphere. It is known that the light scattering in the atmosphere has two types. One is Mie scattering which is caused by particles, such as particles of dust, grit, and water vapor, whose particle diameters are larger than the wavelength of light. Because Mie scattering occurs regardless of the wavelength of light, when Mie scattering occurs, the further an object is from the camera, the more the contrast of the object is reduced, and the object appears white. The other is Rayleigh scattering which is caused by particles, such as air molecules, whose particle diameters are smaller than the wavelength of light. Because, in Rayleigh scattering, the shorter the wavelength of light is, the more strongly the light is scattered, most scattered light that reaches eyes has a blue component, and thus the further an object is, the more the entire object appears blue.
As a technique in which an image whose visibility has been reduced due to scattering is corrected, a technique disclosed in U.S. Pat. No. 8,340,461 has been suggested. In the technique disclosed in U.S. Pat. No. 8,340,461, for each target pixel, contrast is corrected by using an image (dark channel image) obtained by extracting a minimum pixel value among pixel values of all red, green, and blue (RGB) channels in a predetermined region in the vicinity of the target pixel, thereby improving the visibility.
In the technique disclosed in U.S. Pat. No. 8,340,461, however, contrast is corrected without consideration of a difference between two light scattering characteristics of the above-mentioned Mie scattering and Rayleigh scattering, and blue light scattered due to Rayleigh scattering in particular is therefore not corrected sufficiently. Hence, in an image corrected by using the technique disclosed in U.S. Pat. No. 8,340,461, for example, the further an object is, the more the blue tends to be enhanced.